Modular flat-screen color television displays and modules and circuit drives therefor

ABSTRACT

A modular flat-screen color television display having a large area image can be made using an array of modules of easily manufacturable size and preferably removable. The image on each module extends to the edge of the module so that when placed in the array there is no substantial interruption in the television image since the distance between modules is the same as the distance between picture elements within the modules. Control and drive circuitry enable each module to be driven at the same time, thereby decreasing the time it takes to refresh the entire display. The modules contain picture elements which may be emissive, reflective or transmissive.

RELATED APPLICATIONS

This is a divisional of copending application Ser. No. 07/222,523, filedon July 21, 1988.

FIELD OF THE INVENTION

The present invention relates to a flat-screen television display andmore particularly to a flat-screen television display made of moduleswhere the image is uninterrupted by the boundaries between modules.

BACKGROUND OF THE INVENTION

The concept of a large area flat-screen television display which couldbe hung on a wall like a picture has been contemplated since thecommercial introduction of the cathode ray tube television display inthe 1940's. Despite pronouncements throughout the 1950's and 1960's thatflat-screen television display would shortly become a commercialreality, that did not come to pass. The technical problems encounteredin the development caused the cathode ray tube to remain essentially theexclusive way of reproducing video images.

The development of the liquid crystal active matrix flat-screentelevision display at Westinghouse Electric Corporation during the1970's brought new life and substance to flat-screen television. SeeU.S. Pat. No. 3,840,695. This flat-screen display used nematic liquidcrystal as an electro-optic medium which would transmit light, or nottransmit light, depending on the electric potential applied across it.This display consisted of a glass substrate on which an orthogonal array(or "matrix") of thin film transistors, corresponding to pictureelements (or "pixels") in the display, was deposited together withtransparent contact pads spaced in a regular pattern, e.g., 1 millimeteron center, for contacting one surface of the liquid crystal layer.Conductive strips, in rows and columns, were also deposited between thepicture elements over the substrate, the row strips being connected tothe gate electrodes of the transistors and the column strips connectedto the source electrodes of the transistors. The drain electrodes of thetransistors are connected to the contact pads. A second commontransparent contact was placed over the opposite side of the liquidcrystal layer to allow a potential to be applied across it completingthe picture elements of the matrix.

Each picture element of the display could be individually programmed,for each frame of a television picture, to the appropriate brightness,by storing a line of a frame in a peripheral horizontal analog shiftregister disposed at the top of the columns of the display. An entirerow of switching transistors could then be activated by means of avertically disposed digital shift register controlling the rows, whichthen resulted in the transfer of the analog voltage levels stored in theanalog shift register at the top of the columns into the storagecapacitors of that row. By repeating this sequence for each row of thematrix sequentially, in synchronism with the incoming video signal, theentire frame was constructed. In actual practice, the storage capacitorfor each picture element could consist of the liquid crystal layeritself, thus simplifying the driving circuit to a single switchingtransistor at each picture element With an analog shift register, anentire television frame could be generated by the timing and controlcircuit in real time, e.g., 33 msec. Also, the normally sluggish liquidcrystal medium was able to show moving grey scale images of considerableperfection using this configuration. A color display was also producedby placing a patterned red-green-blue filter adjacent the active matrixso that each picture element could also be coordinated with the colorcomponents of a color video signal.

These active matrix liquid crystal flat-screen displays have been andare being made commercially for pocket size televisions. However, theirsize has been limited by the acceptable yield achievable with presentmanufacturing techniques. Typical active matrix liquid crystal displayshave been 2 to 3 inches diagonal, although in development laboratoriesthey have been made up to 10 inches diagonal. The latter, however, havenot been made to my knowledge with acceptable yield. Moreover, even whensuch displays were successfully built, an added problem was the prospectof localized defects occurring in the display which could not beremedied without rejection or replacement of the entire display. Also,such liquid crystal displays needed a retaining wall to confine theliquid crystal in the image forming central area, and outside of thiswall, substantial terminals were needed for each column and row of thematrix for interconnection with column and row driver circuits. For thisreason, modular constructions of such displays were impractical, sincethe image area of each module was bounded by a wide opaque margin. Ithas been proposed to modularize the construction by limiting the columnand row terminals to two or three sides, see U.S. Pat. No. 4,156,833;however, this limited the number of modules for a display typically totwo or at most four, and in turn limited the size of the display.

Modular constructions of very large cathodo-luminescent and liquidcrystal displays have been made for stadiums and the like. Thesedisplays, up to 25×40 meters in size, have been made with a large numberof modules; however, they are characterized by very coarse resolutionresulting from very large picture elements, e.g., one inch square. Theboundaries of the modules in these large panels, particularly thoseconstructed of liquid crystal modules, are visible in the resultingoverall image, and produce a very undesirable effect.

Electroluminescent phosphors have also been contemplated for use inflat-screen television displays. This alternative, however, involvesmore sophisticated electronics. Electroluminescent phosphor displaysoperate at much higher voltages than liquid crystal displays, and insuch an active matrix, two transistors and a capacitor are needed ateach picture element to perform the switching function performed by onetransistor in a liquid crystal display. See U.S. Pat. Nos. 4,006,383,4,042,854 and 4,135,959.

SUMMARY OF THE INVENTION

The present invention is a modular flat-screen television displaycapable of a large area image comprised of an array of modules ofreadily manufacturable size. The modules are of such size to providegood manufacturing yields and small enough to be rejectable orreplaceable at relatively low cost, with the most economical size formanufacture becoming larger as manufacturing techniques improve. Theimage on each module extends to the edge of the module so that whenplaced in the array with similar modules, vertically and horizontally,there is no substantial interruption in the television image produced bythe array. The modules are typically rectangular in shape and are alike,although different shaped and sized modules may be used as desired solong as they mate to form the desired array. The size of the modules isa trade-off against the complexity of the control and drive circuits;the smaller the modules the higher the manufacturing yield and the morecomplex the control and drive circuits for a display of a given size.

The flat-screen television display is comprised of a plurality ofmodules positioned adjacent each other to form an array the size of thedesired flat-screen. Each module has a substrate with first and secondmajor surfaces and edge surfaces. A matrix of picture elements orconductive pads defining picture elements extends over the first majorsurface of the substrate spaced in a regular pattern, with boundarypicture elements or conductive pads adjacent the edge surfaces of thesubstrate to distances such that the regular pattern is continuedsubstantially uninterrupted between adjacent modules.

In each module, a matrix of electrical switching elements extends overthe first major surface of the substrate with each switching elementcapable of activating a picture element or conductive pad upon receivingelectrical signals through both row and column conductive strips. Therow and column conductive strips each extend over the first majorsurface from adjacent an edge surface to adjacent an opposite edgesurface of the substrate such that each switching element can beelectrically activated by a row conductive strip and a column conductivestrip. Preferably, at least one set of row and one set of columnconductive strips are provided adjacent picture elements side-by-sidewhile retaining the corresponding distance between picture elements ofthe matrix. An electrical drive circuit is also positioned adjacent thesecond major surface of the substrate and capable of electricallyactivating the switching elements in correspondence to desired videoimages to be reproduced by the picture elements over the first majorsurface of the substrate. Finally, each module has interconnectingconductors, preferably adjacent the edge surface of the substrate,electrically connecting the drive circuit adjacent the second majorsurface with the row and column conductive strips along the first majorsurface, and is electrically insulated from like interconnectingconductive strips on adjacent modules.

The picture elements of the modules may be emissive, reflective ortransmissive. Where emissive picture elements are employed, suitableelectroluminescent phosphor powders are: for blue color, ZnS,Cu:Br orZnS,Cu:I; for green color, ZnS,Cu:Br with more Cu:Br than for blue; foryellow color, Zn₀.9 Cd₀.1 S,Cu:Br or Zn₀.9 Mn₀.1 S,Cu:Br or Zn₀.7 Cd₀.3S,Cu:Br; and for red color, ZnSe,Cu:Br, ZnSe₀.9 S₀.1,Cu:Br or Zn₀.7Cd₀.3 S,Cu:Br, together with a red dye overlay filter. The phosphorpowder is dispersed in a binder with a high dielectric constant.Alternatively, electroluminescent films consisting, for example, ofZnS:Sm for red color, ZnS:Tb for green color and SrS:Ce for blue colorcould be used for emissive picture elements. Alternatively forreflective picture elements, electrostatic display devices with variableflexibility can be used such as those described in U.S. Pat. Nos.3,897,997, 3,989,357, 4,105,294, 4,266,339, 4,336,536, and 4,168,663.

Alternatively, and preferably, however, the picture elements are eitherreflective or transmissive elements comprised of a light modulating filmcomposed of a liquid crystal dispersion in a polymeric binder. Suitablefilms are described in U.S. Pat. Nos. 4,435,047 and 4,688,900. Ifreflective, each module has a mirror surface on the first major surfaceof the substrate over which the picture elements, switching elements andconductive strips are positioned, preferably with an opaque mask layerin the areas of conductive strips and switching elements to improve thecontrast of the reproduced video picture. If transmissive, a lightsource for one or more modules is positioned adjacent the second majorsurface of the substrate, and a frame is formed as an extension of theedge surfaces of the substrate and capable of transmitting the lightthrough the substrate. The light source may in some transmissionembodiments, as desired, be common to all modules in the array, and thedrive circuit for each module is more specifically positioned adjacentthe frame. Alternatively, separate light sources are provided for eachmodule surrounded by the frame and each module has a backer boardpositioned adjacent the light source opposite the second major surfaceof the substrate to enclose the light source.

In still other alternative embodiments, the light modulating film is notpart of the module but rather separately provided as part of the flatscreen display. In these embodiments, the light modulating film ispositioned adjacent a first major surface formed by the array ofmodules, and a transparent electrode is positioned in contact with afirst major surface of the light modulating film opposite from the firstmajor surface of the array of modules. The modules have conductive padsthat define the picture elements and contact a second major surface ofthe light modulating film opposite from the first major surface to formthe picture elements in the light modulating film.

In addition, whether such picture elements are transmissive orreflective, to be able to reproduce color television pictures, a colorfilter is preferably positioned adjacent the picture elements of thematrix so that only one color will be displayed by each picture element,typically red, green or blue for a standard color television signal. Thenumber of picture elements in such a color display of given size istypically increased by three-fold over a similar black and white displayto provide similar picture quality. There is not necessarily, however,for a one-to-one correspondence between red, green and blue pictureelements, and where there is such correspondence, the colors are notnecessarily in alternate rows or columns of the module.

The flat-screen television is also comprised of an electrical controlcircuit capable of categorizing incoming television picture signalscorresponding to the modules in the array and directing the electricalsignals to the drive circuits of each module according to the portion ofthe television picture to be reproduced by the picture elements of thatmodule. Preferably, the electrical control circuit comprises a decodercircuit and an image processor. The decoder circuit operates on theinput video signal and separates it into at least two parts, onecontaining the video data or information and the other containing thevideo synchronizing signals. If the input video signal is of a colorimage, the decoder preferably separates it into a video signal for eachcolor, typically a red video signal, a green video signal and a bluevideo signal. Decoder circuits are well known in the television fieldand any number of them can be used. For the purpose of the presentinvention, the decoder circuit transforms the input video signal intothe appropriate video signals needed by the image processor.

The image processor, as its name implies, is the electronic circuitrywhich processes the video signals to direct the appropriate signals tothe electrical drive circuits of the appropriate modules at theappropriate times. The image processor uses a timing and control circuitto accomplish this. The timing and control circuit generates a clocksignal and control signals for each module from the synchronizingsignal. The image processor also contains a circuit for storing thevideo signals from the decoder circuit. Preferably each color videosignal is stored digitally in a separate memory capable of holding anentire frame of data. The data is then read out of each memory and fedto the electrical drive circuit of the appropriate module, as describedabove, in response to signals from the timing and control circuit.Preferably this is done in parallel rather than in series so that allmodules are activated at the same time instead of sequentially. It ispossible, however, to read out the stored data in series. The timing andcontrol circuit can be implemented by dedicated hardware or, in whole orin part, by a microprocessor or other computer.

The timing and control circuit determines which and when electricaldrive circuits are activated, thereby activating the switching elementsin the different modules. Preferably, the electrical drive circuitscontain analog and digital switches which control the row and columnconductor strips. Both the row and the column conductor strips connectedto a switching element must be simultaneously activated in order toactivate that switching element at the intersection of a row and columnin the matrix. The number of digital and analog switches used in theelectrical drive circuit and their specific arrangement depend uponwhether the switching elements of the same color are arranged inhorizontal rows or vertical columns or some other pattern, as well aswhether row-at-a-time or column-at-a-time switching is used.

In another embodiment, the video signal is not stored in digital formbut is fed serially to an analog shift register associated with eachmodule which stores the data in an analog form. The video signal is thenfed, in parallel, to each module depending upon the control signals froma timing and control circuit. This simplifies the number and complexityof the circuits required in the electrical control circuit.

"Television" and "video" are used herein in a broad sense to refer tothe reproduction of visual images using electronic signals. Televisionand video includes the reproduction of commercial broadcasting signalsas well as the reproduction of visual images using electronic signalsgenerated from a variety of sources including, but not limited to, videotapes, video disks, microprocessors and other computers.

Other details, objects and advantages of the invention will becomeapparent as the following description of the presently preferredembodiments and presently preferred methods of practicing the inventionproceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, the preferred embodiments of the inventionand preferred methods of practicing the invention are illustrated:

FIG. 1 is an elevational view of the modular flat-screen televisiondisplay of the present invention containing 16 modules in a four-by-fourarray;

FIG. 2 is an elevational view, with portions broken away, of a colormodule preferably of 128×384 pixels suitable for use in the display ofFIG. 1;

FIG. 3 is a cross-sectional view of a module as shown along line 3--3 ofFIG. 2;

FIG. 4a is an enlarged fragmentary elevational view of one corner of themodule shown in FIG. 2, in relation to adjacent similar modules;

FIG. 4b is an enlarged fragmentary elevational view of one corner of themodule corresponding to FIG. 4a showing a different layer of theswitching elements, a layer which defines the picture elements;

FIG. 4c is a cross-sectional view taken along line 4c--4c of FIG. 4b;

FIG. 5 is a fragmentary isometric view of a module as shown in FIG. 2;

FIG. 6 is a back elevational view of a module as shown in FIG. 2;

FIG. 7 is an enlarged fragmentary elevational view of a firstalternative embodiment of one corner of the module as shown in FIG. 2,in relation to adjacent similar modules;

FIG. 8 is an alternative embodiment of the module as shown in FIGS. 2and 3;

FIG. 9 is a cross-sectional view of the module shown in FIG. 8;

FIG. 10 is a cross-sectional view of another alternative embodiment ofthe module shown in FIG. 2;

FIG. 11 is a fragmentary cross-sectional view of a modular flat-screentelevision display of the present invention utilizing the module shownin FIG. 10;

FIG. 12 is an enlarged fragmentary elevational view of a secondalternative embodiment of two corners of the module as shown in FIG. 2,in relation to adjacent like modules;

FIG. 13 is a back elevational view of the modular flat-screen televisiondisplay of FIG. 1;

FIG. 14 is a cross-sectional view taken along line 14--14 of FIG. 13;

FIG. 15 is a block diagram illustrating the electronic circuitry forcontrolling and driving the modular flat-screen television display ofFIG. 1 wherein like color picture elements are arranged in horizontalrows;

FIG. 16 is a block diagram illustrating the electronic circuitry forcontrolling and driving the modular flat-screen television display ofFIG. 1 wherein like color picture elements are arranged in verticalcolumns; and

FIG. 17 is a block diagram illustrating the electronic circuitry forcontrolling and driving the modular flat-screen television display ofFIG. 1 using analog shift registers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Construction Of The Flat-ScreenTelevision Display

Referring to FIG. 1, a flat-screen television display 10, preferablywith color capability, is shown containing sixteen similar modules 11surrounded by decorative frame 12. Modules 11, which are preferablysquare or rectangular for convenient mating, are positioned adjacent toeach other to form a 4×4 array the size of the desired flat-screendisplay 10. The overall size of display 10 will depend on the particularapplication; for convenience for commercial television applications,with a 3:4 aspect ratio, a rectangular display is preferred, and forcomputer applications, with a 1:1 aspect ratio, a square display ispreferred. It is contemplated that modules 11 are preferably about 6×6inches or 6×8 inches, which can be made with satisfactory manufacturingyields, resulting in the 4×4 flat-screen display being 33.9 inches or 40inches diagonal, respectively. Positioned in front of modules 11 inframe 12 is a glass 13 (shown in FIG. 14), possibly of the type toslightly diffuse the picture-element images to provide a better qualitytelevision image. The remainder of the support structure for theflat-screen television display 10 is described later by reference toFIGS. 13 and 14.

Referring to FIGS. 2, 3, 4a, 4b, 4c, 5 and 6, a suitable reflectivemodule 11 for the flat-screen television display 10 is shown in detail.Each module has a substrate 14 (shown in FIG. 3), typically of glass,having first major surface 15, second major surface 16 and edge surfaces17. A matrix of picture elements 18 extends over first major surface 15of substrate 14 in a regular pattern, as best shown in FIG. 2, typicallyin a 128×128 or 144×192 pattern. Picture elements 18 are ofsubstantially the same shape and area so that an observer cannotvisually distinguish a difference in the regular pattern. The boundarypicture elements 18', defined by conductive pads 19 as described below,adjacent the edge surfaces 17 of substrate 14 are positioned from theedge surface 17 such that the regular pattern is substantially continueduninterrupted between adjacent modules as illustrated in FIG. 4b. Thisconfiguration provides a module with, for example, 21 1/3 rows ofpicture elements per inch for a module of 6×6 inches or 6×8 inches. Thepicture elements 18 are preferably formed in a light modulating filmcomposed of a liquid crystal dispersion in a polymeric binder asdescribed in U.S. Pat. Nos. 4,435,047 and 4,688,900, and the pictureelements are defined by conductive pads 19 of switching elements 20 asdescribed below.

Within each module 11, positioned adjacent the picture elements 18 areelectrical switching elements 20 extending over first major surface 15of substrate 14. Each switching element 20 is capable of activating apicture element 18 upon receiving electrical signals through a rowconductive strip 21 and a column conductive strip 22. Alternatively,switching element 20 may be provided by multiplexing with the row andcolumn coordinates applied to opposite sides of a light modulating filmcontaining picture elements 18.

Where a light modulating film is used to provide picture elements 18,each electrical switching element 20 is preferably comprised of a thinfilm transistor 23 having a gate 24 electrically connected to a rowconductive strip 21 and a source 25 electrically connected to a columnconductive strip 22. It should be noted that, using techniqueswell-known in the art, an insulating layer is positioned between theintersection of conductive strips 21 and 22 and between the intersectionof gate 24 and the semiconductor extending from source 25 to drain 27.As a part of each switching element 20, insulating layer 26 is placedover the entire first major surface 15, including conductive strips 21and 22 and transistors 23 except at drains 27 of transistors 23, andthen as shown in FIG. 4c, transparent conductive pads 19 of, forexample, indium tin oxide is placed over the insulating layer 26 incontact with the light modulating film to define picture elements 18 and18' in the light modulating film. Each conductive pad 19 is electricallycharged through the drain 27 of a transistor 23. The electrical circuitof switching element 20 is completed by a transparent conductive layer28 on the opposite surface of light modulating film containing pictureelements 18 and 18' connected to a common ground or to interconnectingconductors as hereinafter described. The latter alternative also allowsthe alternative of allowing the light modulating film common to allmodules 11 in display 10, to which conductive pads 19 of each module inthe array make electrical contact. By this layered arrangement ofswitching elements 20 (shown in FIGS. 4a, 4b and 4c), picture elements18 and 18' can take up a larger area of module 11 and a brightertelevision image can be reproduced.

Row and column conductive strips 21 and 22 each extend over first majorsurface 15 of substrate 14 from adjacent edge surface 17 to adjacent,opposite edge surface 17 such that each electrical switching element 20can be electrically activated by both a row conductive strip 21 or 21'and a column conductive strip 22 or 22'. Each conductive strip 21 and 22also is enlarged in area adjacent edge surface 17 as shown in FIG. 4aand wraps around from first major surface 15 to an edge surface 17, toallow for electrical interconnection with electrical drive circuit 29.Electrical drive circuit 29 is positioned adjacent the second majorsurface 16 of substrate 14 on printed circuit board 44, which is thenlaminated to second major surface 16 of substrate 14 (as shown in FIG.3). Alternatively, electrical drive circuit 29 could be directlypositioned or formed on second major surface 16 of substrate 14, ratherthan on a separate printed circuit board 44 that is then laminated tosecond major surface 16. Electrical drive circuit 29, the positioning ofwhich is best shown in FIG. 6, preferably has a fan-in electricalconnecting configuration to be capable of electrically activating allswitching elements 20 in the module 11 corresponding to the desiredvideo images to be formed by picture elements 18 on first major surface15 of substrate 14.

Interconnecting conductors 30 connect electrical drive circuit 29 to rowconductive strips 21 and 21' and column conductive strips 22 and 22'.Although other embodiments such as feed-through interconnection could beutilized, interconnecting conductors 30 are preferably positioned overedge surfaces 17 (as shown in FIGS. 3 and 5) and wrap around secondmajor surface 16 to electrically connect conductive strips 21, 21', 22and 22' to electrical drive circuit 29. Interconnecting conductors 30can be made by traditional metallization and photolithographictechniques on the adhesive side of a thin, insulating tape typicallyabout one mil in thickness. The insulating tape with interconnectingconductors 30 is preferably placed over edge surfaces 17 after drivecircuit 29 is positioned relative to second major surface 16 ofsubstrate 14. However formed, the interconnecting conductors 30 areelectrically insulated from like interconnecting conductors of adjacentmodules. The thickness of the interconnecting conductors 30 should besuch as to provide uniform spacing, and generally minimal spacing,between modules 11 in the array of display 10 (as shown in FIG. 4a).

Interconnecting conductors 30 may also extend along edge surface 17 to adistance beyond major surface 15 at the corners of each module 11 toelectrically connect conductive layer 28 to electrical drive circuit 29.Alternatively, however, the circuit can be completed by electricallyconnecting conductive layer 28 to a common ground provided, for example,by forming a transparent conductive layer over the inside surface offront glass 13 (FIG. 14) of display 10 to which layer 28 can makeelectrical contact.

Preferably at least one set of row and one set of column conductivestrips 21' and 22' are provided side by side while retaining thecorresponding distance between picture elements 18 of the matrix asshown in FIG. 2. In this embodiment, the corresponding distance betweenpicture elements 18 and 18' of the matrix is maintained since theconductive pads 19 defining the picture elements are in a differentplane from conductive strips 21' and 22'. Conductive pads 19 are aslarge in area as space will permit without extending over conductivestrips 21, 21', 22 and 22'. This arrangement allows conductive strips21' or 22' to avoid running close to an edge surface 17. Theside-by-side row and column conductive strips 21' and 22' may occur onlyonce on each module 11. This requires, however, the use of an asymmetricmask in the formation of the conductive strips, affecting themanufacture of each module 11. It may be appropriate, particularly inembodiments as shown in FIG. 4, where the switching elements 20 are inlayers, as described above, and in turn the spacing between side-by-siderow and column conductive strips can be relatively large, to utilize asymmetric photo mask so that all row and column conductive strips are inside-by-side sets. This pattern, called a "butterfly pattern", wouldrepeat the pairing of conductive strips 21' and 22' over the entiresurface 15 of substrate 14, with the advantage of providing redundantconductive strips and increasing the manufacturing yields of modules 11.

Since the particular module 11 shown in FIGS. 2 through 6 is areflective embodiment capable of reproducing color television images, amirrored surface 31 is provided on first major surface 15 of substrate14 over which picture elements 18, switching elements 20 and conductivestrips 21, 21', 22 and 22' are positioned. Preferably, an opaque masklayer is then provided in the areas of the conductive strips and thethin film transistors to improve the contrast of the reproduced videopicture. Also, to allow for the reproduction of color images, colorfilter 32 (FIGS. 3 or 9) is positioned between picture elements 18 andfirst major surface 15 of substrate 14. Color filter 32 typically hasred, green and blue components with these primary colors alternatingover picture elements 18 by rows or columns, or other conventionedconfigurations such as color triplets or quads. Each picture element 18corresponds with one of the primary colors to produce that colorcomponent of a color television image to be reproduced. The color filter32 can alternatively have other positions in the module than shown inFIG. 3, such as adjacent conductive layer 28. It should not, however, bepositioned spaced-apart from the picture element 18 to avoid lightparallax.

The flat-screen color television display of FIG. 1 also has anelectrical control circuit capable of categorizing incoming electricalpicture signals as to the corresponding modules 11 in the array anddirecting the electrical signals to electrical drive circuits 29 on eachmodule 11 corresponding to the portion of the television picture to bereproduced by picture elements 18 on that module 11. The specifics ofthe electronic drive and control circuitry are described later,beginning on page 23.

In some embodiments, each module 11 can be removed from the array of thedisplay shown in FIG. 1, and replaced by a like module 11. To facilitatethis, handles 33 are provided on the back of each module 11 as shown inFIG. 6. By being removable, the flat-screen television display can berepaired with relatively low cost if a localized defect develops in thedisplay.

Referring to FIG. 7, an alternative embodiment for module 11 is shownwhere the matrix of switching elements 20 is made in one layer ratherthan three as described above with reference to FIGS. 4a, 4b and 4c.Specifically, conductive pads 19, typically of indium tin oxide toprovide transparency, are in the same layer as the thin film transistor23. This requires that each conductive pad 19, which is in contact withthe light modulating film and defines a picture element 18 be spacedfrom conductive strips 21, 21', 22 and 22' and transistor 23, except fordrain 27 thereof which electrically powers the conductive pad 19. Again,as previously explained, the light modulating film may be common to allmodules 11 in display 10 or part of each module 11. This embodiment hasthe advantage of reducing the number of manufacturing steps in makingmodules 11 and particularly the switching elements 20 for the modules11. However, it has the disadvantage of reducing the area correspondingto the first major surface 15 of the substrate which is available forthe picture elements 18. Each conductive pad 19 defining a pictureelement 18 is substantially the same to avoid the observer from visuallydetecting irregularities in the pattern of the matrix of pictureelements 18. The difference in area between this embodiment and thatwith the multiple layer switching element 20 can be seen by comparingFIGS. 4 and 7. However, even in this embodiment, for presently availableresolution, the area of module 11 available for use as picture elements18 is approximately 55% of the total area corresponding to major surface15 of substrate 14, compared with 30% of the corresponding area of acathode ray tube display which is currently used for reproducing colortelevision images.

Referring to FIGS. 8 and 9, an alternative embodiment of module 11 thatis transmissive is shown. In this embodiment, substrate 14, pictureelements 18, switching elements 20 and color filter 32 are all the sameas alternatively described above with reference to FIGS. 2 through 6. Inthis embodiment there is not a mirrored surface 31. Rather, light source34 is positioned adjacent second major surface 16 of substrate 14. Lightsource 34 is surrounded by frame 35 positioned adjacent surfaces 17 ofsubstrate 14 and having edge surfaces 36 which are extensions of edgesurfaces 17 of substrate 14. Frame 35 is a transparent plastic, such asPerspex™, capable of transmitting light from light source 34 tosubstrate 14 and providing a support for substrate 14. Backer board 37is positioned adjacent light source 34 opposite second major surface 16of substrate 14 and has electrical drive circuits 29 positioned on it.Further, interconnecting conductors 30 adjacent edge surfaces 17 ofsubstrate 14 extend over edge surfaces 36 of frame 35 electricallyconnecting drive circuit 29 on backer board 37 with row and columnconductive strips 21, 21', 22 and 22' adjacent first major surface 15 ofsubstrate 14. Again, interconnecting conductors 30 are electricallyinsulated from like interconnecting conductors of adjacent modules. Thedifference between this transmissive embodiment module 11 and thereflective embodiment of module 11 can be seen by comparison of FIGS. 3and 9. Again, as described above, the light modulating film may be madepart of display 10 common to all modules 11 to which the conductive pads19 of each module 11 electrically connect, or made separately a part ofeach module 11.

Referring to FIGS. 10 and 11, a further alternative embodiment of module11 that is transmissive is shown. In this embodiment, module 11 does notcontain the light source 34, but rather light source 34 is common to allmodules 11 in the display 10. In addition, electrical drive circuit 29is positioned more specifically adjacent edge surfaces 36 of frame 35and backer board 37 is spaced from module 11 and is common to allmodules in display 10. The electrical connection from an electricalcontrol circuit (not shown) to drive circuit 29 is made through alattice-type plug 38 into which modules 11 can be inserted andelectrical connection made, and removed to form display 10. Thisembodiment has the advantage of providing more uniform backlighting withlight source 34 common over display 10. Common light source 34 provideslight through frame 35 capable of transmitting light to substrate 14.The other aspects and alternatives of the construction of this moduleare those described above with reference to FIGS. 8 and 9.

Referring to FIG. 12, an emissive embodiment of module 11 and itsrelation to like modules in a display 10 is shown. In this embodiment,an electroluminescent phosphor layer of appropriate color or colorsforms picture elements 18 in contact with conductive pads 19, instead ofa light modulating film. The construction of module 11 is otherwisesubstantially the same as described with reference to FIGS. 4a, 4b and4c, except that color filter 32 may be used depending on theavailability of appropriate electroluminescent phosphors to form colors,and that conductive pads 19 can be metallic (nontransparent), preferablywith the upper surface able to reflect radiation emitted from thepicture element 18 toward the front viewing surface of display 10.Electrical connections of drive circuit 29 to the row and columnconductive strips 21 and 22 are also the same as described above withreference to FIGS. 4a, 4b and 4c. The switching elements 20 in thisembodiment differ, however, in that each contains a second thin filmtransistor 39 and a storage capacitor 40. Gate 41 of second thin filmtransistor 39 is electrically connected to drain 27 of thin filmtransistor 23 and to the storage signal side of capacitor 40. Drain 42of second thin film transistor 39 is connected to conductive pad 19which in turn is a terminal of electroluminescent picture element 18.Source 43 of second thin film transistor 39 and the other terminal ofstorage capacitor 40 are electrically connected to the adjacent rowconductive strip 21. Capacitor 40 is a three-layer structure with thetop layer (shown in FIG. 12) the storage signal side and the bottomlayer the feed signal side connected to conductive strips 21, with aninsulating layer to maintain capacitance between them.

In this embodiment, the vertical scan register of the electrical controlcircuit (described later) includes means for connecting a given rowconductive strip 21 to the vertical scan switching signal input, whileconnecting all other row conductive strips 21 to a reference signalwhich is typically at ground level. This arrangement permitssimultaneous application of a uniform reference signal and aninformation signal applied by column conductive strips 22 to pictureelement 18 and also permits a return path for the current flowingthrough the electroluminescent picture elements 18 from the conductivelayer 28. The common reference level is normally connected to the powersupply to complete the circuit. This arrangement for switching elements20 provides an active matrix circuit suitable to switch thesubstantially higher voltages that are needed for control ofelectroluminescent phosphor picture elements 18. The high voltage, thinfilm transistors used in this embodiment are preferably made usingcadmium selenide with a thicker insulator layer between thesemiconductor film and the gate electrode.

Referring to FIGS. 13 and 14, the support structure for the flat-screentelevision display shown in FIG. 1 is detailed. This support structureis particularly adapted to allow for removal of modules 11 and repair ofthe display 10 during manufacture, testing and subsequent use. Bolts 50are threaded through the sides of frame 12 and contact, by pads 51,individual rows and columns in the 4×4 array of modules 11 inflat-screen television display 10. Bolts 50 through pads 51 and theopposite side of frame 12 exert a compressive force on the modules 11 tohold them in close contact. Also, to hold the modules 11 in positionagainst glass 13 hinged bars 52 are provided for each row of modules 11on array. Individual resilient pads 53 are positioned on each bar 52 toexert an oppressive force against the back of modules 11 thereby forcingthem against the glass 13. The bars 52 are also hinged at 54 andattached by other suitable fasteners 55 at the opposite end to frame 12.

When it is desired to replace a module 11 in the flat-screen televisiondisplay, fastener 55 is loosened and bar 52 corresponding to the row inwhich the module 11 that is to be replaced is located is swung away.Bolts 50 for both the column and row in which the module to be replacedis located are then loosened and the module removed from the array and alike module put in its place. The bolts 50 are then retightened, the bar52 swung in position and then fastened with fastener 55.

Electronic Drive Circuitry For Modular Flat-Screen Televisions.

Conventional video signals are time sequential signals consisting of ahigh speed serial analog data stream. Typically, an image or frame isbuilt up using a number of horizontal lines that are laid downconsecutively. The lines may be laid down sequentially or in aninterlaced manner. In the latter case, the odd numbered lines of theimage are laid down by a first scan, and then a second scan lays downthe even numbered lines. This process can be done on a panel-wide basisor on a per module basis. The electrical control circuit for aflat-screen television display generates the correct sequence ofenabling signals to activate the electrical drive circuits and directthe video signal to the appropriate horizontal rows and vertical columnsof the entire display or of each module.

In one embodiment the electrical switching elements of the modules areaddressed a row at a time by activating an entire horizontal row ofpicture elements in a module simultaneously and applying the appropriateportion of the sampled video signal corresponding to the pictureelements 18 for that row of that module 11 to all of the columns of thatmodule 11. The process is then repeated row-by-row, module-by-moduleuntil the entire display 10 has been addressed. For purpose ofexplanation, FIG. 2 shows some of the rows and columns which will beactivated. At the start of a frame, row 1 of the first module would beactivated and the first 128 samples of the video signal would beswitched into the first 128 picture elements thereof at the same time.Then row 1 of the second module would be activated and the next 128samples of the video signal would be switched into the first 128 pictureelements thereof. The same process would be repeated for the third andfourth modules. For a sequential video signal, this process would berepeated in sequence with row 2 being activated so that samples of thevideo signal are switched to the second 128 picture elements in each ofthe first four modules. Row 2 of the second, third and fourth modulesare similarly activated. This process is repeated until all of thepicture elements 18 in the first four modules have been activated. Tocomplete the frame, this process is repeated for the fifth to eighth,ninth to twelfth and finally the thirteenth to sixteenth modules. For aninterlaced video signal, the second rows to be activated would be thethird rows of the modules. After all the odd rows had been filled forthe frame, the process would repeat for the even rows of all themodules. Alternatively, at the start of a frame, the first rows of thefirst four modules could be activated at the same time and the first 512(4×128) samples of the video signal could be switched into the first 128picture elements in each module simultaneously. Then the second row ofthe first four modules would be activated and the next 512 samples ofthe video signal could be simultaneously switched into the second 128picture elements of each module. This process is similar to the onedescribed above for activating each module except that four modules aretreated as a unit so that the frame is filled on a panel basis ratherthan a module basis.

Unfortunately, the rate at which the serial video signal arrives and,therefore, the rate at which it must be sampled generally exceeds therate at which the modules can accept the video data samples. It is,therefore, necessary to use a storage device to store the data from theincoming video signal and pass portions thereof to the appropriatemodules in parallel. The storage devices for each module can form partof the electrical drive circuits, can be part of the electrical controlcircuit, or both. When the storage devices are part of the electricaldrive circuits, it is convenient to make the number of data samplesstored equal to the number of picture elements in one row of one module.Since it takes time to transfer the data samples from the storage deviceto the module, it is often necessary to use two sets of storage devicesand store the samples in one memory while the previously stored datasamples are being transferred from another memory to the module. Due tothe row selection process, if only one row of the entire display 10 isactivated at a given time, all of the corresponding column elements ofeach column of modules can be connected in parallel and only two storagedevices or memories are needed for each column of the entire display 10.

Preferably, digital serial-input parallel-output shift registers areused as the storage devices in this configuration. To obtain asatisfactory gray scale, a minimum of 6-bits is necessary and it wouldbe preferable to use 8-bits. Making the storage devices in this wayrequires the use of an analog-to-digital converter at the input to thestorage device and a digital-to-analog converter for each of theparallel outputs. The analog-to-digital converter could be made to serveboth sets of storage devices, but digital-to-analog converters would berequired for every element of both sets of storage devices. One set ofdigital-to-analog converters could possibly be used, but complicatedswitching would be needed at both the input and the output of thedigital-to-analog converters.

This method of activation can be implemented by known electroniccircuitry. While it is similar to what is currently done for flat-screentelevision, it fails to take advantage of the modularization of thepresent invention. It is preferable to present the video data to allmodules simultaneously. This would simplify the control circuitry anddecrease the required response time. In order to achieve the desiredserial to parallel transformation of the video data, the data must firstbe stored in a memory. Several methods are known, but the mostadvantageous from a data-integrity and manipulative standpoint is totransform the analog video data into a digital form and store it a frameor a field at a time. This permits all the modules of the display to beupdated at the same time, thus providing a significant relief on theupdating speed required for each module since an entire frame period isavailable for such updating instead of just that portion of the frameperiod which corresponds to the image portion displayed by theparticular module. Thus, if there are n modules in total, then theupdate time available for each module is increased by the factor n,compared with the serial updating of the screen described above. Thisparallel addressing of all the modules is a unique advantage of thepresent invention.

Typical television "frame grabbers" have only one serial analog signalinput and one serial analog signal output for displaying a full frame.The circuitry of the present embodiment is capable of accepting theincoming serial video data and generating multiple analog output signalsso that data can be presented to all modules simultaneously. Thisenables the video signal information to be provided to the modulessimultaneously instead of sequentially. For a color video display, theentire frame is preferably stored as three separate video frames (oneper color), and the video data for each color is presented to themodules as a number of parallel data streams.

In standard television signals, color images are represented asluminance, hue and saturation data which can be decomposed into thethree primary colors red, blue and green. This information can beextracted from standard video signals such as NTSC, PAL or SECAM byconventional techniques, such as multiplexing. Preferably, a decodercircuit, which is well known in the art, performs this function. In thepreferred embodiment as shown in FIG. 15, the extracted red, blue andgreen analog video signals from the decoder circuit are each digitizedin an image processor 56 by means of an analog-to-digital converter(ADC) 57 and are each stored digitally as successive bytes of data, onecorresponding to each picture element in a frame. The data for eachcolor is stored in separate random access memories (RAM) 58, which sendthe video data to each module as needed. Preferably, there are twomemories for each color which are dual ported. While one memory is beingupdated serially at the frame rate, the other memory is being read outin a serial-parallel mode at the module rate. This allows each module tobe updated independently of the other modules. In order to display thedigitally stored data in a parallel fashion on a per module basis, itmust be converted back into an analog signal. This can be accomplishedby using a digital-to-analog converter (DAC) 59 with a digital latch foreach module in the system.

Using an image processor such as shown in FIG. 15 has the addedadvantage that the bandwidth needed for addressing and driving themodules is reduced by a factor of n where n is the modularity factor.Thus, if the video bandwidth is 20 MHz and there are 16 modules (n =16),then each module would have a video bandwidth of only 1.25 MHz, greatlyalleviating the speed requirements on the active matrix and theelectrical drive circuit 29 of each module. It should also be noted thatthe price of digital memory is continually decreasing and very largememories with fast access times are currently available at a low cost.This is another reason for having the memory be part of the imageprocessor 56 rather than part of the drive circuits 29 on modules 11.

In the updating process, the three colors can be presented to eachmodule, in parallel, or the colors can be scanned sequentially on a permodule or a per panel basis. By presenting the colors in sequence, theanalog portion of the electronics required for the electrical drivecircuit 29 of each module can be reduced by a factor of three. (CompareFIGS. 15 and 16). In FIG. 16, three columns, one for each color pictureelement and each having an analog switch 60 need to be driven. Thisresults in the number of analog switches 60 being three times the numberof digital switches 61. In FIG. 15, however, only one column with oneanalog switch 60 needs to be driven while the three colors are presentedsequentially with a successive row being enabled for each color. Thismode of operation essentially involves forming rows, instead of columns,of the colors red-green-blue, and requires the scanning of three linesof each module for each line of the video input. If the colors arepresented in parallel on all the columns (strips), then three times asmany column strips are needed, but the row scan rate is reduced by afactor of three. The color sequential solution is preferred. Thisreduces the number of analog switches 60 needed to drive the columnstrips while increasing the number of digital switches 61 needed for therow strips by a factor of three. However, since digital switches 61 areeasier to realize, this alternative gives an overall cost saving. Thehigher required row scan rate is not a serious drawback: if there are,for example, 16 modules, in a 4×4 array as illustrated in FIG. 1, thisarrangement will result in a row scan rate which is 3/4 of the videorate, and a column scan rate which is 1/12 of the video rate, resultingin a reduction to 3/4×1/12=1/16 of the original video rate.

A further reduction in the rate at which information is actuallytransferred to the picture elements 18 of each module 11 can be achievedif all picture elements in a given row of a module are addressedsimultaneously, i.e., if row-at-a-time addressing as discussed above isemployed. This can be accomplished through using charge-coupled devices(CCD), bucket-brigade devices or other appropriate means in an analogshift-register configuration such as shown in FIG. 17, rather thananalog switches as shown in FIG. 16. Although there are today nocommercially available analog shift-registers which accept serial dataas inputs and output parallel data, the design and fabrication of suchintegrated circuits is certainly within the capability of currenttechnology. This approach would have the advantage of further reducingthe speed of addressing individual picture elements by a factor equal tothe number of picture elements in each row of a module, e.g., 128. Acombination of analog shift-register and analog holding register 63 canbe used to permit simultaneous readout, in parallel, of one line of datawhile the succeeding line of data is being clocked into theshift-register from the image processor 56.

As previously discussed, the three colors can be presented from theimage processor 56 to the modules 11 either in parallel or sequentially.The embodiment shown in FIG. 17 contemplates parallel transfer of thecolor information from the image processor 56 to the modules 11,analogous to the technique illustrated in FIG. 16. An alternativeembodiment of the method illustrated in FIG. 17 which is analogous tothe technique illustrated in FIG. 15 is possible and in fact preferredsince it reduces the number of analog shift registers 63 for each module11 from three to one while increasing the number of digital switches 61from X to 3X.

It is the purpose of the timing and control circuit 62, shown in FIGS.15 and 16, to generate all of the necessary clocking and gating waveforms needed by the A/D converters 57, memories 56, D/A converters 59,digital switches 61, analog switches 62 and analog shift registers 63 toeffect proper processing and routing of the incoming video picturesignal to the correct picture elements on display 10. The clocking andgating wave forms must be synchronized to the incoming video signal.This is generally accomplished by having an accurate master clockoperating at a high multiple of the horizontal input frequency andprecisely synchronized to the horizontal input frequency. This clocksignal, along with the horizontal and vertical synchronizing inputsignals, controls a variety of digital counters. Appropriate logicalcombinations of the decoded counter outputs can produce all of therequired clocking and gating wave forms. Implementation of suchcircuitry involves standard phase locked loop, counter and logic circuittechnology well known in the art. Alternative to using counters andspecific logic circuitry, a microprocessor running from the master clockcan be employed to generate the required timing and control signals.

The modular flat television screen, driven by the electronic systemdescribed above, can be considered as a sophisticated color videodisplay monitor. By conventional, present day techniques it can be usedto present standard television broadcast signals, signals generated byvideo cassette recorders or computers. With suitable, state-of-the-artelectronics, it will also permit the mixing and presentation of severalvideo signals derived from different broadcast or other sources, anddifferent portions of the screen could show different programssimultaneously if desired. Through a link to a microcomputer equippedwith suitable software, the screen could also be used as a canvas forgenerating artwork by the users, or for the playing of electronic games.Another novel possibility is to display, in a stationary mode,reproductions of famous paintings (e.g., Mona Lisa or Primavera or VanGogh's Irises), stored on "art video tapes", thus the sitting room couldhave a different "theme picture" each season or day of the week while itis not used as a receiver. Other innovative uses may well be found inthe future.

Although the invention has been described in detail in the foregoing forpurposes of illustration, it is to be understood that such details aresolely for that purpose and that variations may be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention are described in the following claims.

What is claimed is:
 1. A flat-screen color television displaycomprising:A. a plurality of modules positioned adjacent each other toform an array the size of the desired flat-screen display; B. each ofsaid modules having a substrate with first and second major surfaces andedge surfaces and being capable of transmitting light, a matrix ofpicture elements extending over the first major surface of the substratein a regular pattern with boundary picture elements adjacent the edgesurfaces of the substrate to a distance such that the regular pattern iscontinued substantially uninterrupted between adjacent ones of saidmodules, where said picture elements are formed of a thin filmdispersion of liquid crystal droplets in a polymeric medium, a matrix ofelectrical switching elements extending over the first major surface ofthe substrate with each of said switching elements capable of activatinga picture element upon receiving electrical signals through both row andcolumn conductive strips, a color filter positioned adjacent the pictureelements such that a color video image can be displayed by the module,said row and column conductive strips each extending over the firstmajor surface of said substrate from adjacent an edge surface toadjacent an opposite edge surface of the substrate such that said eachswitching element can be electrically activated by a row conductivestrip and a column conductive strip; C. a light source positionedadjacent the second major surface of the substrate of at least onemodule in the array; D. an electrical drive circuit positioned adjacentthe second major surface of said substrate and capable of electricallyactivating the switching elements in correspondence to desired visualimages to be formed by the picture elements over the first major surfaceof said substrate; E. interconnecting conductors adjacent the edgesurfaces of the substrate and electrically connecting the drive circuitwith the row and column conductive strips on the first major surface ofsaid substrate and electrically insulated from similar interconnectingconductors of an adjacent module; and F. an electrical control circuitcapable of separating incoming video signals corresponding to themodules in the array and directing the electrical signals to the drivecircuit of said each module according to the portion of the televisionpicture to be reproduced by the picture elements on that module.
 2. Aflat-screen color television display as described in claim 1 wherein thecolor filter is positioned between the picture elements and the firstmajor surface of the substrate.
 3. A flat-screen color televisiondisplay as described in claim 1 wherein the picture elements arepositioned between the color filter and the first major surface of thesubstrate.
 4. A flat-screen color television display as described inclaim 1 wherein said each module can be removed from the matrix andreplaced by another like module.
 5. A flat-screen color televisiondisplay as described in claim 1 wherein at least one set of said row andone set of said column conductive strips are provided side-by-sidespaced from an edge surface while retaining the corresponding distancesbetween said picture elements of the regular pattern.
 6. A flat screencolor television display as described in claim 1 wherein a common lightsource is provided for the array of modules, and the electrical drivecircuit for said each module is positioned more specifically adjacent aframe forming an extension of the edge surfaces of said each module. 7.A flat screen color television display as described in claim 1 whereinsaid light source is provided for said each module surrounded by a frameforming an extension of the edge surfaces of each said substrate, andthe electrical drive circuit for said each module is positioned on abackboard positioned adjacent to the light source opposite the secondmajor surface of the substrate to enclose the light source.
 8. Aflat-screen color television display as described in claim 1 wherein thedesired visual image is simultaneously and sequentially presented by theelectrical control circuit to the electrical drive circuit of said eachmodule.
 9. A flat-screen color television display as described in claim1 wherein that portion of the desired visual image corresponding to onemodule is fed sequentially to the electrical drive circuit of thatmodule from the electrical control circuit while at the same time allthe modules are being driven in parallel.
 10. A flat-screen colortelevision display as described in claim 1 wherein the electricalcontrol circuit comprises a decoder circuit and an image processor andwherein each said electrical drive circuit comprises a plurality ofanalog and digital switches for activating the switching elements inresponse to sequential signals from the image processor simultaneouslyfed to each electrical drive circuit.
 11. A flat-screen color televisiondisplay as described in claim 10 wherein the image processor furthercomprises: an analog-to-digital converter, for transforming an analogvideo signal to a digital signal which can be easily stored; a memoryfor storing one frame of the video signal in digital form; adigital-to-analog converter for generating an analog video signal forsaid each module; and a timing and control circuit for simultaneouslydirecting different portions of the analog video signal to said eachmodule.
 12. A flat-screen color television display as described in claim11 wherein the number of said analog-to-digital converters correspondsto the number of colors in the display and there are two memories foreach color.
 13. A flat-screen color television display as described inclaim 12 wherein there is one said digital-to-analog converter for saideach module.
 14. A flat-screen color television display as described inclaim 10 wherein analog switches activate the column conductors anddigital switches activate the row conductors of the switching elements.15. A flat-screen color television display as described in claim 14wherein there are three times as many digital switches as analogswitches.
 16. A flat-screen color television display as described inclaim 14 wherein there are three times as many analog switches asdigital switches.